Methods and systems for selecting capture verification modes

ABSTRACT

Methods and systems are directed to selecting from a variety of capture verification modes. A plurality of capture verification modes, including a beat by beat capture detection mode and a capture threshold testing mode without intervening beat by beat capture detection is provided. An efficacy of at least one of the capture verification modes is evaluated, and based on the evaluation, a capture verification mode is selected.

RELATED PATENT DOCUMENTS

This application is a continuation of U.S. patent application Ser. No.12/697,853, filed Feb. 1, 2010, now U.S. Pat. No. 8,271,087, which is acontinuation of U.S. patent application Ser. No. 11/168,276, filed onJun. 28, 2005, now U.S. Pat. No. 7,657,314, the entire disclosures ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to capture verification, andmore particularly to selecting between capture verification modes usedin connection with cardiac pacing.

BACKGROUND OF THE INVENTION

When functioning normally, the heart produces rhythmic contractions andis capable of pumping blood throughout the body. However, due to diseaseor injury, the heart rhythm may become irregular resulting in diminishedpumping efficiency. Arrhythmia is a general term used to describe heartrhythm irregularities arising from a variety of physical conditions anddisease processes. Cardiac rhythm management systems, such asimplantable pacemakers and cardiac defibrillators, have been used as aneffective treatment for patients with serious arrhythmias. These systemstypically comprise circuitry to sense electrical signals from the heartand a pulse generator for delivering electrical stimulation pulses tothe heart. Leads extending into the patient's heart are connected toelectrodes that contact the myocardium for sensing the heart'selectrical signals and for delivering stimulation pulses to the heart inaccordance with various therapies for treating the arrhythmias.

Cardiac rhythm management systems including pacemakers operate tostimulate the heart tissue adjacent to the electrodes to produce acontraction of the tissue. Pacemakers are cardiac rhythm managementsystems that deliver a series of low energy pace pulses timed to assistthe heart in producing a contractile rhythm that maintains cardiacpumping efficiency. Pace pulses may be intermittent or continuous,depending on the needs of the patient. There exist a number ofcategories of pacemaker devices, with various modes for sensing andpacing one or more heart chambers.

When a pace pulse produces a contraction in the heart tissue, theelectrical cardiac signal preceding the contraction is denoted thecaptured response (CR). The captured response typically includes anelectrical signal, denoted the evoked response signal, associated withthe heart contraction, along with a superimposed artifact signalassociated with residual post pace polarization at the electrode-tissueinterface. The magnitude of the residual post pace polarization signal,or pacing artifact, may be affected by a variety of factors includinglead polarization, after-potential from the pace pulse, lead impedance,patient impedance, pace pulse width, and pace pulse amplitude, forexample.

A pace pulse must exceed a minimum energy value, or capture threshold,to produce a contraction. It is desirable for a pace pulse to havesufficient energy to stimulate capture of the heart without expendingenergy significantly in excess of the capture threshold. Thus, accuratedetermination of the capture threshold is required for efficient paceenergy management. If the pace pulse energy is too low, the pace pulsesmay not reliably produce a contractile response in the heart and mayresult in ineffective pacing.

If the pacemaker delivers pacing pulses having an energy thatsignificantly exceed the capture threshold, the patient may experiencediscomfort and the battery life of the device will be shorter.Determining the capture threshold of the heart allows adjustment of thepacing energy to a level that reliably produces capture withoutunnecessary energy expenditure.

SUMMARY OF THE INVENTION

The present invention is directed to a method and system for selectingcapture verification modes. In accordance with one embodiment, a cardiactherapy method includes selection of capture verification modes. Themethod requires providing a plurality of capture verification modes,where at least a first capture verification mode includes an automaticbeat-by-beat capture detection, and a second capture verification modeincludes capture threshold testing without intervening beat by beatcapture detection. The efficacy of at least one of the provided captureverification modes is evaluated and, based on the evaluation, a captureverification mode is selected.

In a further embodiment of the invention, a cardiac rhythm managementsystem may be configured to implement a variety of capture verificationmodes. The cardiac rhythm management system includes electrodes capableof electrically coupling to a heart, a pulse generator coupled to theelectrodes for delivering pacing pulses to the heart, circuitry forimplementing a plurality of capture verification modes, and a processorfor evaluating and selecting the capture verification modes. Circuitryfor implementing capture verification modes includes automatic capturedetection (ACD) circuitry for implementing a beat by beat automaticcapture detection mode, and capture threshold testing (CTT) circuitryfor implementing a capture threshold testing mode without interveningcapture detection.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flowchart of a method for selecting captureverification modes in accordance with embodiments of the invention;

FIGS. 2 and 3 are state diagrams illustrating capture verification modeselection in accordance with embodiments of the invention;

FIG. 4 is a block diagram of a system that may be used to implementcapture verification mode selection in accordance with embodiments ofthe invention;

FIG. 5 is a partial view of one embodiment of an implantable medicaldevice in accordance with embodiments of the invention;

FIG. 6 is a block diagram of an implantable medical device that may beused to verify capture using automatic capture verification modes inaccordance with embodiments of the invention; and

FIG. 7 is a block diagram of capture verification mode selectioncircuitry in accordance with embodiments of the invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail below. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents, and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In the following description of the illustrated embodiments, referencesare made to the accompanying drawings that form a part hereof, and inwhich is shown by way of illustration, various embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural and functional changes may bemade without departing from the scope of the present invention.

After delivery of a pacing pulse to a heart chamber, various cardiacresponses to the pacing pulse are possible. For example, the pacingpulse may generate a propagating wavefront of depolarization resultingin a contraction of the heart chamber. In such an instance, the pacingpulse is said to have captured the heart chamber. Capture of the heartchamber may occur if the pacing pulse has sufficient energy to initiatethe depolarization wavefront and is delivered during a period of timethat the cardiac tissue is non-refractory. If the pacing pulse does notproduce contraction of the cardiac tissue, the cardiac response isreferred to as non-capture. It is desirable for a pace pulse to havesufficient energy above the capture threshold to capture the heartwithout expending excess energy above the capture threshold.

Whether an applied electrical pacing stimulus captured the heart may bedetermined by evaluating the post-pace electrical signal produced by theheart. The process of evaluating the heart's electrical signals may beperformed automatically, for example, using systems havingpatient-implantable and/or patient-external circuitry and/or components.

In one implementation, an implantable cardiac rhythm management (CRM)device, such as a pacemaker or other implantable device, may be used toautomatically evaluate the electrogram signals produced by the heart todetermine the cardiac response to a pacing pulse. For example, animplantable cardiac rhythm management device may determine the cardiacresponse to a pacing pulse using electrogram signals on a beat to beatbasis.

In another implementation, the cardiac response to pacing may beevaluated using a patient-external computing system such as an advancedpatient management (APM) system. Advanced patient management systems mayinvolve one or more distinct medical devices that are accessible throughvarious communications technologies. Patient and/or device informationmay be acquired by the one or more medical devices and downloadedperiodically or on command to a patient information server. Thephysician and/or the patient may communicate with the medical devicesand/or the patient information server, for example, to access patientdata, to modify device parameters, and/or to initiate, terminate oradjust processes, e.g., therapy and/or diagnostic processes, performedby the medical devices or the patient information server.

Embodiments of the invention are directed to methods and systems forselecting a cardiac verification mode used for determining the capturethreshold of one or more cardiac chambers, e.g., atrial and/orventricular chambers. The capture threshold is defined as the lowestpacing energy that consistently captures the heart. A capture thresholddetermined by the selected capture verification mode is used to adjustthe pacing energy delivered to the patient so that pacing is provided atan energy level that reliably produces capture without unnecessaryenergy expenditure. In various embodiments described herein, selectingthe capture verification mode involves selecting between independentcapture verification modes, such as an automatic beat-to-beat capturedetection (ACD) mode, a capture threshold testing (CTT) mode, a trendonly mode with a physician programmed output with daily measurement, orno capture verification. In further embodiments, selection of a captureverification mode may be based on a physician selected or pre-determinedhierarchy.

The automatic capture detection (ACD) mode may be used, for example, tomonitor capture results in one or more of a left atrium, right atrium,left ventricle, and right ventricle on a beat-by-beat basis. In oneexample, the ACD process may involve adjusting the pacing thresholdafter detecting loss of capture. For example, if loss of capture isdetected by the ACD process, the pacing energy may be ramped up over oneor more beats until capture is detected.

In another example, if loss of capture is detected by the ACD process, athreshold search is triggered. The threshold search involves deliveringpacing pulses at variable energy levels to determine the capturethreshold. The capture threshold determined by the threshold search isused to set the pacing energy. Automatic capture detection (ACD) modemay additionally involve controlling back up pacing when a pace pulsedelivered to the heart fails to produce a captured response. A back uppace may be delivered, for example, about 70-80 ms after the initialpace pulse.

A patient's capture threshold may fluctuate significantly during thefirst weeks after implantation. Soon after implantation, the capturethreshold typically increases to a peak value and then graduallydecreases. Eventually, the capture threshold becomes relatively stableat a level higher than the initial implantation threshold but less thanthe peak value. Various physiological factors may cause fluctuations inthe capture threshold level after implantation, including, for example,illness, changes in the lead/tissue interface, or use of medication.

The use of ACD mode allows the capture threshold to be adjustedfrequently to correspond to variations in the capture threshold of thepatient. In some implementations, the pacing energy may be adjustedafter every beat. In other implementations, the pacing energy may beadjusted after a threshold search is performed following a detected lossof capture. When operating in ACD mode, the frequency of thresholdsearches may be limited to a predetermined frequency. For example, inone scenario, threshold searches are performed about once per hour andpacing energy adjustment may occur after each threshold search.

The frequency of pacing energy adjustment allows ACD mode to closelytrack variations in the patient's capture threshold. When operatingeffectively, ACD mode provides consistent pacing using a pacing energyjust above the capture threshold, for example, 0.2-0.5 volts above thecapture threshold. Setting the pacing energy slightly above the capturethreshold provides a safety margin to ensure consistent pacing. Theability to closely match the pacing energy to the capture thresholdusing a smaller safety margin advantageously provides an increasedbattery life.

However, in some situations, reliable beat by beat capture detectionrequired for effective operation of ACD mode may be difficult to obtainor maintain. Unreliable capture detection may be caused, for example, bya high occurrence of intrinsic or fusion beats, by changes inphysiologic conditions, by device programming incompatible with capturedetection, by system noise, or by other factors. In these situations,operating in ACD mode may cause more frequent backup pacing and morefrequent threshold searches. After loss of capture is detected in ACDmode, the device may operate in a high energy pacing default mode untila threshold search is performed. Thus, when ACD mode is ineffective, thebattery longevity savings associated with pacing at a lower safetymargin may not be realized.

Another capture verification mode that may be selected involvesperforming a sequence of threshold searches that occur according to atime schedule. Capture threshold testing (CTT) mode may be used todetermine the capture threshold in any or all of the left atrium, rightatrium, left ventricle, and right ventricle. In CTT mode, a thresholdsearch may be performed according to a regular periodic time schedule,e.g., once per day, once every 21 hours, performed according to a randomtime schedule, or performed according to some other schedule. The pacingenergy is adjusted based on the capture threshold determined by one ormore of the most recent capture threshold measurements. In oneimplementation, a capture threshold test may be automatically initiatedby the pacemaker or by the APM system according to a predetermined timeschedule, for example. In another implementation, the APM system mayrequest a series of tests leading up to a scheduled device follow-upvisit (in-office or remote). In yet another implementation, a thresholdsearch may be initiated by a command to the pacemaker from a physicianor other person.

The threshold search comprises delivering a sequence of pacing pulses toa heart chamber and determining if the pacing pulses capture the heartchamber. The energy of the pacing pulses delivered by the thresholdsearch may be decreased in discrete steps until a predetermined numberof loss-of-capture events occur. Upon detection of loss of capture, thestimulation energy may be increased in discrete steps until apredetermined number of capture events occur to confirm the capturethreshold. Other procedures for implementing capture threshold searchingmay be utilized. In one example, the pacing energy may be increased indiscrete steps until capture is detected. In another example, the pacingenergy may be adjusted according to a binomial search pattern.

In some scenarios, the threshold searches are ineffective and anaccurate capture threshold cannot be obtained. If CTT mode is unable toprovide an accurate capture threshold, the system may revert to adefault mode that involves pacing at a relatively high voltage withoutcapture verification. The pacing energy used for the default modeinvolves a large margin of safety making this operation in the defaultmode more energy consumptive than either ACD mode or CTT mode.Alternatively, the system may transition to a physician programmedoutput that includes a daily threshold measurement, known as a trendonly mode.

FIG. 1 is a flowchart illustrating a cardiac therapy method involvingselection of a capture verification mode in accordance with embodimentsof the invention. A plurality of capture verification modes is provided110. As previously discussed, the plurality of modes may include anautomatic capture detection (ACD) mode comprising beat to beat capturedetection and a (CTT) mode comprising a sequence of periodicallyperformed threshold searches.

At least one of the plurality of capture verification modes is evaluated120 with respect to efficacy in delivering an appropriate level ofcapture verification benefit to the patient. For example, an efficacymeasure may include a performance metric. A capture verification mode,e.g., ACD mode or CTT mode, may be selected 130 based on the evaluation.In addition, in some embodiments, the selected mode may be a fixedvoltage mode or a trend only mode. The selected capture verificationmode is used to monitor the capture threshold of the patient.

In accordance with some embodiments, evaluating the efficacy of acapture verification mode and selecting one of the plurality of captureverification modes may be performed automatically by implantable CRMdevices or by advanced patient management (APM) systems. According tosome embodiments, assessing the efficacy and selecting the captureverification mode may be performed manually. In one implementation, datarelated to capture verification mode efficacy may be acquired by apacemaker and transferred to an APM server. A physician or other personmay review the collected data, select a capture verification mode basedon the collected data, and communicate with the pacemaker via the APMserver to select an appropriate capture verification mode.

FIG. 2 is a state diagram 200 illustrating various processes involved inselecting a capture verification mode in accordance with embodiments ofthe invention. Transitions into or out of the modes 210, 220, 230illustrated in diagram 200 may be implemented manually by a physician ormay be implemented by a device that is programmed to perform theselection process automatically or on command. Transitioning betweencapture verification modes 210, 220, and 230 allows the captureverification mode to be modified based on dynamically changing patientconditions. The capability to select between capture verification modesprovides device operation that increases battery longevity without acompromising patient safety.

For purposes of describing the capture verification mode selectionprocess, it is assumed that the device initially operates in ACD mode210. While operating in ACD mode 210, pacing pulses are delivered at apacing energy that is a relatively small margin, e.g., about 0.5 V,above the capture threshold. After each pace, the system determines ifthe pacing pulse captured the heart tissue. For each non-captured beat,the device may deliver a back-up pace. The energy of the back-up pace issufficiently high to ensure capture. In some implementations, theback-up pace is delivered at a maximum energy level, e.g., 5 V.

If loss of capture is detected, or of other factors are detected thatmay disrupt capture detection, a threshold search is performed. If acapture threshold cannot be determined by the threshold search, or ifloss of capture persists as determined by beat to beat capturedetection, the device may revert 226 to a fixed voltage mode 230 withoutcapture verification. Periodically, while pacing in the fixed voltagemode 230, a threshold search may be conducted. If a capture threshold isacquired by the threshold search, then the device may transition 235 tooperate in ACD mode 210. If a capture threshold is not acquired by thethreshold search, then the device remains in the fixed voltage mode 230.

While operating in ACD mode 210, the efficacy of the ACD mode 210 isassessed. Under some conditions, while operating in ACD mode 210, thebenefits of ACD mode may not be realized. For example, the benefits ofACD mode may not accrue if one or more of the following factors ispresent: the frequency of backup pacing is high, the retry rate ofthreshold searches is high, atrial fibrillation is detected, theAV-delay programming is incompatible with ACD mode, an elevated capturethreshold is present, low percentage of ventricular paces, and/or otherconditions affecting the efficacy of ACD mode. These factors may beperiodically evaluated. If the evaluation indicates that the benefits ofACD mode are not being realized, and/or that operation in CTT mode 220is likely to enhance patient safety as compared to an ACD mode 210, CTTmode 220 may be selected which triggers a transition 215 into CTT mode220.

In CTT mode 220, threshold searches are performed periodically, e.g.,every 21 hours or according to another time schedule. If a thresholdsearch is successful, the pacing energy is adjusted based on one or moremost recent threshold searches? For example, the pacing energy may beadjusted to about twice the most recent capture threshold or to about 2volts, whichever is higher. The pacing safety margin used whileoperating in CTT mode may be greater than the safety margin used for ACDmode. An increased pacing safety margin is necessary because beat tobeat automatic capture detection is not used in CTT mode. Thus to ensurecontinuous therapeutic pacing support to the patient, the pacingthreshold must be high enough to provide consistent pacing betweenthreshold searches, e.g., about 21 hours.

If one or more threshold searches are unsuccessful, the device mayrevert to 227 to the fixed voltage mode 230 without captureverification. Periodically, a threshold search may be conducted while infixed voltage mode 230. If a capture threshold is acquired by thethreshold search, then the device may begin 236 operating in CTT mode220. If a capture threshold is not acquired by the threshold search,then the device remains in the fixed voltage mode 230.

The efficacy of operating in CTT model 220 is assessed. If it is likelythat benefits associated with ACD mode 210, such as battery longevity,improved patient safety, and/or other benefits, are likely to berealized in ACD mode 210, then ACD mode 210 may be selected and thedevice transitions 225 into ACD mode. The factors used to evaluate thelikelihood that the benefits of ACD mode 210 will be accrued maycomprise, for example, the absence of fusion beats detected duringthreshold searches, high signal to noise ratio on the channel used forcapture detection, AV-delay programming compatible with ACD mode,results of AV search or Reverse mode switch algorithms, history ofatrial tachycardia mode switch response, or relatively low capturethreshold, among other factors.

In some embodiments, the device may store information associated withcapture verification mode transitions for further evaluation. The storedinformation may be transmitted to a separate computing device, such asan APM system, for further evaluation or trending.

FIG. 3 illustrates state diagram illustrating a capture verificationmode selection process in accordance with embodiments of the invention.According to this embodiment, pacing may be delivered to a patient inACD mode 310, CTT mode 320, or fixed voltage mode 330. To facilitate thediscussion, it is assumed that the device is initially operating in ACDmode 310. Pacing is delivered to the patient at a pacing voltage abovethe capture threshold, for example the capture threshold plus about 0.5volts. Beat by beat, the device senses for an evoked response anddetermines 315 if the cardiac pacing response is a captured response ora non-captured response.

Periodically, e.g., about every 21 hours, or if the device detectscertain conditions, e.g., loss of capture, noise on the channel used todetect capture, and low capture threshold, e.g., less than about 2 mV,signal to artifact (SAR) ratio of less than about 2, the device mayperform a threshold search 311 to determine the capture threshold. Ifany of the conditions listed above are detected, but a threshold searchwas previously performed within a predetermined period, for exampleabout 1 hour, the device may enter a retry state 312 wherein the devicewaits for a period of time, for example, until about an hour has passedsince the previous threshold search. The device performs one or morethreshold searches 311 to attempt to determine the capture threshold.For example, the device may perform a sequence of threshold searches 311such as one threshold search performed per hour. If a threshold searchis successful, the device resumes beat to beat capture detection 315.

However, if the threshold searches 311 are unsuccessful, or aresuccessful but indicate a capture threshold lower than a predeterminedthreshold for safe pacing, transition to a fixed voltage mode 330 mayoccur. When operating in the fixed voltage mode 330, the system paces ata high output pace energy, for example, about twice the capturethreshold or about 3.5 volts, whichever is higher. The system continuesto attempt to acquire a capture threshold by periodically performingthreshold searches 311. In one implementation, for example, while in thefixed voltage mode 330, threshold searches 311 may be performed aboutonce every week.

The efficacy of the ACD mode 310 is evaluated. The efficacy evaluationof the ACD mode 310 may involve determining if the benefits of ACD mode310 are realized while the device is operating in ACD mode 310. Forexample, frequent backup pacing, frequent threshold searches, frequentreversion to or extended time in fixed voltage mode pacing are factorsindicating the benefits of ACD mode are possibly not realized. Frequenthigh energy pacing negates any gain to battery longevity while in ACDmode and may be equivalent to setting a fixed pacing amplitude.

According to one embodiment, a transition from ACD mode 310 to CTT mode320 may occur under one or more of the following conditions: 1) thefrequency of threshold searches exceeds a predetermined threshold, 2)the frequency of back up paces delivered exceeds a predeterminedthreshold; 3) the time spent in fixed voltage mode 330 and/or in theretry state 312 exceeds a predetermined threshold. If any one or more ofthese conditions meet the respective threshold criteria, or if otherconditions are present that indicate ACD mode is ineffective, CTT mode325 may be selected.

The efficacy evaluation may be performed manually or automatically. Inone implementation, the efficacy evaluation occurs according to apredetermined time schedule. If the efficacy evaluation indicates thatACD mode 310 is not effective and the capture verification mode shouldbe changed, then CTT mode 320 may be selected.

In another implementation, the efficacy evaluation is updatedcontinuously by the device each time a significant event occurs, e.g., athreshold search is performed, back up pace delivered, or the deviceremains in retry or fixed voltage mode.

When operating in the CTT mode 320, the device delivers 325 pacingpulses at a pacing energy that is greater than the pacing energy used inACD mode 310. For example, the pacing energy may be set to the greaterof either about two times a previously determined capture threshold orabout 2 volts. Beat to beat capture detection is not performed afterdelivery of the pacing pulses.

In one implementation, while operating in CTT mode 325, thresholdsearches 321 are performed once every 21 hours, however, other random orregular time schedules may be used to schedule the threshold searches.If the threshold search 321 is successful then the device continues 325to deliver pacing without beat to beat capture detection and withperiodic threshold searches 321 to set the pacing energy.

If a threshold search 321 fails, the system transitions into a retrystate 322. While in the retry state 322, the pacing energy is based, forexample, on one or more of the previously successful capture thresholdsacquired. When it is time for a threshold search to be performed, thedevice transitions from the retry state 322 and the threshold search 321is performed. For example, after one hour in retry mode 322, a thresholdsearch 321 may be conducted. If the threshold search 321 is successful,then the device may resume pacing 325 in CTT mode 320.

If a predetermined number, for example about 3, threshold searches 321yield unsuccessful capture threshold results, or if the threshold searchresults are lower than a minimum threshold, a transition to fixedvoltage pacing mode 330 may occur.

The efficacy of the capture verification mode may be periodicallyevaluated to determine whether re-entry into ACD mode 310 from CTT mode320 is desirable. For example, the various factors may be evaluated todetermine the likelihood of beneficial operation in ACD mode 310. In oneimplementation, if battery life would likely be increased by operationin ACD mode 310, then ACD mode 310 is selected and the devicetransitions from CTT mode 320 operation to ACD mode 310 operation.

FIG. 4 is a block diagram of a medical system that may be used inconjunction with an advanced patient management (APM) system toimplement a capture verification mode selection process in accordancewith embodiments of the invention. The medical system may include, forexample, one or more patient-internal medical devices 420 and one ormore patient-external medical devices 430. Each of the patient-internal420 and patient-external 430 medical devices may include one or more ofa patient monitoring unit 427, 437, a diagnostics unit 429, 439, and/ora therapy unit 428, 438. Capture verification circuitry 410, inaccordance with embodiments of the invention, may include circuitryimplementing various capture verification modes, circuitry for assessingthe efficacy of capture verification modes, a controller for selectingone or none of the capture verification modes, a timing circuit, and amemory, for example. Components of the capture verification circuitry410 may be housed in a patient internal medical device 420, a patientexternal medical device 430, and a remote network server system such asadvanced patient medical (APM) system 440 or in any combination of theabove-mentioned devices 420, 430, 440.

Selection of the capture verification modes in accordance with variousembodiments of the invention may be performed automatically by thecapture verification circuitry or manually by a physician or otherperson using information provided by the medical system. In oneimplementation, the internal device 420 may comprise a pacemaker thatcomprises all components of the capture verification circuitry. Thepacemaker evaluates the efficacy of a capture verification mode selectsa capture verification mode based on the efficacy evaluation.

In another implementation, the pacemaker comprises circuitry forimplementing ACD mode and CTT mode. The pacemaker communicates with anAPM server that houses the selection processor. Based on data acquiredby the pacemaker and transmitted to the APM server, the selectionprocessor circuitry evaluates the efficacy of a capture verificationmode selects a capture verification mode based on the efficacyevaluation. The APM system communicates the selection to the pacemakerand the pacemaker may modify the capture verification mode used forpacing based on the selection.

In yet another implementation, data associated with capture verificationmode efficacy may be downloaded from a pacemaker 420 and stored at anAPM patient information server 440. The physician and/or the patient maycommunicate with the patient information server 440, for example, to theview or otherwise acquire the data associated with capture verificationmode efficacy. The physician or other person may select a captureverification mode based on the capture verification mode efficacy data.The selection is communicated to the pacemaker 420 for implementationvia a wireless communication channel

The patient-internal medical device 420 may be a fully or partiallyimplantable device that performs monitoring, diagnosis, and/or therapyfunctions. The patient-external medical device 430 may performmonitoring, diagnosis and/or therapy functions external to the patient(i.e., not invasively implanted within the patient's body). Thepatient-external medical device 430 may be positioned on the patient,near the patient, or in any location external to the patient. It isunderstood that a portion of a patient-external medical device 430 maybe positioned within an orifice of the body, such as the nasal cavity ormouth, yet can be considered external to the patient (e.g., mouthpieces/appliances, tubes/appliances for nostrils, or temperature sensorspositioned in the ear canal).

The patient-internal and patient-external medical devices 420, 430 maybe coupled to one or more sensors 421, 422, 431, 432, patient inputdevices 424, 434 and/or other information acquisition devices 426, 436.The sensors 421, 422, 431, 432, patient input devices 424, 434, and/orother information acquisition devices 426, 436 may be employed to detectconditions relevant to the monitoring, diagnostic, and/or therapeuticfunctions of the patient-internal and patient-external medical devices420, 430.

The medical devices 420, 430 may each be coupled to one or morepatient-internal sensors 421, 431 that are fully or partiallyimplantable within the patient. The medical devices 420, 430 may also becoupled to patient-external sensors 422, 432 positioned on the patient,near the patient, or in a remote location with respect to the patient.The patient-internal 421, 431 and patient-external 422, 432 sensors maybe used to sense conditions, such as physiological or environmentalconditions, that affect the patient.

The patient-internal sensors 421 may be coupled to the patient-internalmedical device 420 through implanted leads. In one example, an internalendocardial lead system is used to couple sensing electrodes to animplantable pacemaker or other cardiac rhythm management device. One ormore of the patient-internal sensors 421, 431 may be equipped withtransceiver circuitry to support wireless communication between the oneor more patient-internal sensors 421, 431 and the patient-internalmedical device 420 and/or the patient-external medical device 430.

The patient-external sensors 422, 432 may be coupled to thepatient-internal medical device 420 and/or the patient-external medicaldevice 430 through leads or through wireless connections.Patient-external sensors 422 preferably communicate with thepatient-internal medical device 420 wirelessly. Patient-external sensors432 may be coupled to the patient-external medical device 430 throughleads or through a wireless link.

The medical devices 420, 430 may be coupled to one or more patient-inputdevices 424, 434. The patient-input devices 424, 434 facilitate manualtransfer of information to the medical devices 420, 430 by the patient.The patient input devices 424, 434 may be particularly useful forinputting information concerning patient perceptions or patient-knownfactors, such as patient smoking, drug use, or other factors that arenot automatically sensed or detected by the medical devices 420, 430. Inone implementation, a device programmer may be used to facilitatepatient input to a medical device 420, 430.

The medical devices 420, 430 may be connected to one or more informationsystems 426, 436, for example, a database that stores information usefulin connection with the monitoring, diagnostic, or therapy functions ofthe medical devices 420, 430.

In one embodiment, the patient-internal medical device 420 and thepatient-external medical device 430 may communicate through a wirelesslink between the medical devices 420, 430. For example, thepatient-internal and patient-external devices 420, 430 may be coupledthrough a short-range radio link, such as Bluetooth or a wireless link.The communications link may facilitate uni-directional or bi-directionalcommunication between the patient-internal 420 and patient-external 430medical devices. Data and/or control signals may be transmitted betweenthe patient-internal 420 and patient-external 430 medical devices tocoordinate the functions of the medical devices 420, 430.

The patient-internal medical device 420 and/or the patient-externalmedical device 430 may be coupled through a wireless or wiredcommunications link to a patient information server that is part of anadvanced patient management (APM) system 440. The APM patientinformation server 440 may be used to download and store data collectedby the patient-internal and patient-external medical devices 420, 430.

The data stored on the APM patient information server 440 may beaccessible by the patient and the patient's physician through terminals450, e.g., remote computers located in the patient's home or thephysician's office. The APM patient information server 440 may be usedto communicate to one or more of the patient-internal andpatient-external medical devices 420, 430 to effect remote control ofthe monitoring, diagnosis, and/or therapy functions of the medicaldevices 420, 430. For example, after the physician selects a captureverification mode, then the APM system may communicate the selection tothe appropriate medical device to effect the change in captureverification mode.

In one scenario, the patient-internal and patient-external medicaldevices 420, 430 may not communicate directly with each other, but maycommunicate indirectly through the APM system 440. In this embodiment,the APM system 440 may operate as an intermediary between two or more ofthe medical devices 420, 430. For example, data and/or controlinformation may be transferred from one of the medical devices 420, 430to the APM system 440. The APM system 440 may transfer the data and/orcontrol information to another of the medical devices 420, 430.

Although the present system is described in conjunction with animplantable cardiac defibrillator having a microprocessor-basedarchitecture, it will be understood that the implantable cardiacdefibrillator (or other device) may be implemented in any logic-basedintegrated circuit architecture, if desired.

Referring now to FIG. 5 of the drawings, there is shown a cardiac rhythmmanagement (CRM) device that may be used to implement captureverification methods of the present invention. The CRM device 500 iselectrically and physically coupled to a lead system 502. Captureverification circuitry 700, such as the capture verification circuitrydescribed in connection with FIG. 7, and elsewhere herein, may bedisposed within the housing of the CRM device 500. The housing and/orheader of the CRM device 500 may incorporate one or more electrodes 608,609 used to provide electrical stimulation energy to the heart and tosense cardiac electrical activity. The CRM device 500 may utilize all ora portion of the CRM system housing as a can electrode 609. The CRMdevice 500 may include an indifferent electrode positioned, for example,on the header or the housing of the CRM device 500. If the CRM device500 includes both a can electrode 609 and an indifferent electrode 608,the electrodes 608, 609 typically are electrically isolated from eachother.

The lead system 502 is used to detect electric cardiac signals producedby the heart 501 and to provide electrical energy to the heart 501 undercertain predetermined conditions to treat cardiac arrhythmias. The leadsystem 502 may include one or more electrodes used for pacing, sensing,and/or defibrillation. In the embodiment shown in FIG. 5, the leadsystem 502 includes an intracardiac right ventricular (RV) lead system504, an intracardiac right atrial (RA) lead system 505, an intracardiacleft ventricular (LV) lead system 506, and an extracardiac left atrial(LA) lead system 508. The lead system 502 of FIG. 5 illustrates oneembodiment that may be used in connection with the cardiac responseclassification methodologies described herein. Other leads and/orelectrodes may additionally or alternatively be used.

The lead system 502 may include intracardiac leads 504, 505, 506implanted in a human body with portions of the intracardiac leads 504,505, 506 inserted into a heart 501. The intracardiac leads 504, 505, 506include various electrodes positionable within the heart for sensingelectrical activity of the heart and for delivering electricalstimulation energy to the heart, for example, pacing pulses and/ordefibrillation shocks to treat various arrhythmias of the heart.

As illustrated in FIG. 5, the lead system 502 may include one or moreextracardiac leads 508 having electrodes, e.g., epicardial electrodes,positioned at locations outside the heart for sensing and pacing one ormore heart chambers.

The right ventricular lead system 504 illustrated in FIG. 5 includes anSVC-coil 516, an RV-coil 514, an RV-ring electrode 511, and an RV-tipelectrode 512. The right ventricular lead system 504 extends through theright atrium 520 and into the right ventricle 519. In particular, theRV-tip electrode 512, RV-ring electrode 511, and RV-coil electrode 514are positioned at appropriate locations within the right ventricle 519for sensing and delivering electrical stimulation pulses to the heart.The SVC-coil 516 is positioned at an appropriate location within theright atrium chamber 520 of the heart 501 or a major vein leading to theright atrial chamber 520 of the heart 501.

In one configuration, the RV-tip electrode 512 referenced to the canelectrode 609 may be used to implement unipolar pacing and/or sensing inthe right ventricle 519. Bipolar pacing and/or sensing in the rightventricle may be implemented using the RV-tip 512 and RV-ring 511electrodes. In yet another configuration, the RV-ring 511 electrode mayoptionally be omitted, and bipolar pacing and/or sensing may beaccomplished using the RV-tip electrode 512 and the RV-coil 514, forexample. The right ventricular lead system 504 may be configured as anintegrated bipolar pace/shock lead. The RV-coil 514 and the SVC-coil 516are defibrillation electrodes.

The left ventricular lead 506 includes an LV distal electrode 513 and anLV proximal electrode 517 located at appropriate locations in or aboutthe left ventricle 524 for pacing and/or sensing the left ventricle 524.The left ventricular lead 506 may be guided into the right atrium 520 ofthe heart via the superior vena cava. From the right atrium 520, theleft ventricular lead 506 may be deployed into the coronary sinusostium, the opening of the coronary sinus 550. The lead 506 may beguided through the coronary sinus 550 to a coronary vein of the leftventricle 524. This vein is used as an access pathway for leads to reachthe surfaces of the left ventricle 524 which are not directly accessiblefrom the right side of the heart. Lead placement for the leftventricular lead 506 may be achieved via subclavian vein access and apreformed guiding catheter for insertion of the LV electrodes 513, 517adjacent to the left ventricle.

Unipolar pacing and/or sensing in the left ventricle may be implemented,for example, using the LV distal electrode referenced to the canelectrode 609. The LV distal electrode 513 and the LV proximal electrode517 may be used together as bipolar sense and/or pace electrodes for theleft ventricle. The left ventricular lead 506 and the right ventricularlead 504, in conjunction with the CRM device 500, may be used to providecardiac resynchronization therapy such that the ventricles of the heartare paced substantially simultaneously, or in phased sequence, toprovide enhanced cardiac pumping efficiency for patients suffering fromchronic heart failure.

The right atrial lead 505 includes a RA-tip electrode 556 and an RA-ringelectrode 554 positioned at appropriate locations in the right atrium520 for sensing and pacing the right atrium 520. In one configuration,the RA-tip 556 referenced to the can electrode 609, for example, may beused to provide unipolar pacing and/or sensing in the right atrium 520.In another configuration, the RA-tip electrode 556 and the RA-ringelectrode 554 may be used to effect bipolar pacing and/or sensing.

FIG. 5 illustrates one embodiment of a left atrial lead system 508. Inthis example, the left atrial lead 508 is implemented as an extracardiaclead with LA distal 518 and LA proximal 515 electrodes positioned atappropriate locations outside the heart 501 for sensing and pacing theleft atrium 522. Unipolar pacing and/or sensing of the left atrium maybe accomplished, for example, using the LA distal electrode 518 to thecan 609 pacing vector. The LA proximal 515 and LA distal 518 electrodesmay be used together to implement bipolar pacing and/or sensing of theleft atrium 522.

Referring now to FIG. 6, there is shown an embodiment of a cardiacrhythm management (CRM) system 600 suitable for implementing a captureverification methodology of the present invention. FIG. 6 shows a CRMsystem 600 divided into functional blocks. It is understood by thoseskilled in the art that there exist many possible configurations inwhich these functional blocks can be arranged. The example depicted inFIG. 6 is one possible functional arrangement. Other arrangements arealso possible. For example, more, fewer or different functional blocksmay be used to describe a cardiac defibrillator suitable forimplementing the methodologies for verifying capture using a number ofcapture verification modes in accordance with methods of the presentinvention. In addition, although the CRM system 600 depicted in FIG. 6contemplates the use of a programmable microprocessor-based logiccircuit, other circuit implementations may be utilized.

The CRM system 600 depicted in FIG. 6 includes circuitry for receivingcardiac signals from a heart and delivering electrical stimulationenergy to the heart in the form of pacing pulses or defibrillationshocks. In one embodiment, the circuitry of the CRM system 600 isencased and hermetically sealed in a housing 601 suitable for implantingin a human body. Power to the CRM system 600 is supplied by anelectrochemical battery 680. A connector block (not shown) is attachedto the housing 601 of the CRM system 600 to allow for the physical andelectrical attachment of the lead system conductors to the circuitry ofthe CRM system 600.

The CRM system 600 may be a programmable microprocessor-based system,including a control system 620 and a memory 670. The memory 670 maystore information associated with capture verification mode selection,along with other information. The memory 670 may be used, for example,for storing historical EGM and therapy data. The historical data storagemay include data obtained from long term patient monitoring used fortrending or other diagnostic purposes. Historical data, as well as otherinformation, may be transmitted to an external programmer unit 690 asneeded or desired.

The control system 620 and memory 670 may cooperate with othercomponents of the CRM system 600 to control the operations of the CRMsystem 600. The control system depicted in FIG. 6 incorporates a captureverification circuitry 700 for evaluating an efficacy of captureverification modes and selecting from a variety of capture verificationmodes or a high output fixed voltage mode in accordance with variousembodiments of the present invention. The control system 620 may includeadditional functional components including a pacemaker control circuit622, an arrhythmia detector 621, and a template processor for cardiacsignal morphology analysis, along with other components for controllingthe operations of the CRM system 600.

Telemetry circuitry 660 may be implemented to provide communicationsbetween the CRM system 600 and an external programmer unit 690. In oneembodiment, the telemetry circuitry 660 and the programmer unit 690communicate using a wire loop antenna and a radio frequency telemetriclink, as is known in the art, to receive and transmit signals and databetween the programmer unit 690 and the telemetry circuitry 660. In thismanner, programming commands and other information may be transferred tothe control system 620 of the CRM system 600 from the programmer unit690 during and after implant. In addition, stored cardiac datapertaining to capture threshold, capture detection and/or cardiacresponse classification, for example, along with other data, may betransferred to the programmer unit 690 from the CRM system 600.

In the embodiment of the CRM system 600 illustrated in FIG. 6,electrodes RA-tip 556, RA-ring 554, RV-tip 512, RV-ring 511, RV-coil514, SVC-coil 516, LV distal electrode 513, LV proximal electrode 517,LA distal electrode 518, LA proximal electrode 515, indifferentelectrode 608, and can electrode 609 are coupled through a switch matrix610 to sensing circuits 631-637.

A right atrial sensing circuit 631 serves to detect and amplifyelectrical signals from the right atrium of the heart. Bipolar sensingin the right atrium may be implemented, for example, by sensing voltagesdeveloped between the RA-tip 556 and the RA-ring 554. Unipolar sensingmay be implemented, for example, by sensing voltages developed betweenthe RA-tip 556 and the can electrode 609. Outputs from the right atrialsensing circuit are coupled to the control system 620.

A right ventricular sensing circuit 632 serves to detect and amplifyelectrical signals from the right ventricle of the heart. The rightventricular sensing circuit 632 may include, for example, a rightventricular rate channel 633 and a right ventricular shock channel 634.Right ventricular cardiac signals sensed through use of the RV-tip 512electrode are right ventricular near-field signals and are denoted RVrate channel signals. A bipolar RV rate channel signal may be sensed asa voltage developed between the RV-tip 512 and the RV-ring 511.Alternatively, bipolar sensing in the right ventricle may be implementedusing the RV-tip electrode 512 and the RV-coil 514. Unipolar ratechannel sensing in the right ventricle may be implemented, for example,by sensing voltages developed between the RV-tip 512 and the canelectrode 609.

Right ventricular cardiac signals sensed through use of the RV-coilelectrode 514 are far-field signals, also referred to as RV morphologyor RV shock channel signals. More particularly, a right ventricularshock channel signal may be detected as a voltage developed between theRV-coil 514 and the SVC-coil 516. A right ventricular shock channelsignal may also be detected as a voltage developed between the RV-coil514 and the can electrode 609. In another configuration the canelectrode 609 and the SVC-coil electrode 516 may be electrically shortedand a RV shock channel signal may be detected as the voltage developedbetween the RV-coil 514 and the can electrode 609/SVC-coil 516combination.

Outputs from the right ventricular sensing circuit 632 are coupled tothe control system 620. In one embodiment of the invention, rate channelsignals and shock channel signals may be used to develop morphologytemplates for analyzing cardiac signals. In this embodiment, ratechannel signals and shock channel signals may be transferred from theright ventricular sensing circuit 632 to the control system 620 and to atemplate processor where the morphological characteristics of a cardiacsignal are analyzed for arrhythmia detection.

Left atrial cardiac signals may be sensed through the use of one or moreleft atrial electrodes 515, 518, which may be configured as epicardialelectrodes. A left atrial sensing circuit 635 serves to detect andamplify electrical signals from the left atrium of the heart. Bipolarsensing and/or pacing in the left atrium may be implemented, forexample, using the LA distal electrode 518 and the LA proximal electrode515. Unipolar sensing and/or pacing of the left atrium may beaccomplished, for example, using the LA distal electrode 518 to canvector 609 or the LA proximal electrode 515 to can vector 609.

A left ventricular sensing circuit 636 serves to detect and amplifyelectrical signals from the left ventricle of the heart. Bipolar sensingin the left ventricle may be implemented, for example, by sensingvoltages developed between the LV distal electrode 513 and the LVproximal electrode 517. Unipolar sensing may be implemented, forexample, by sensing voltages developed between the LV distal electrode513 or the LV proximal electrode 517 to the can electrode 609.

Optionally, an LV coil electrode (not shown) may be inserted into thepatient's cardiac vasculature, e.g., the coronary sinus, adjacent theleft heart. Signals detected using combinations of the LV electrodes,513, 517, LV coil electrode (not shown), and/or can electrodes 609 maybe sensed and amplified by the left ventricular sensing circuitry 636.The output of the left ventricular sensing circuit 636 is coupled to thecontrol system 620.

The outputs of the switching matrix 610 may be operated to coupleselected combinations of electrodes 511,512, 513, 514, 515, 516, 517,518, 556, 554 to various sensing circuits 631-636. An evoked responsesensing circuit 637 may be used to sense and amplify voltages developedusing various combinations of electrodes. An evoked response sensingcircuit 637 may be used to sense cardiac signals indicative of a cardiacresponse to pacing, e.g., capture or non-capture. Cardiac signalsindicative of the cardiac pacing response are sensed and amplified bythe evoked response circuit 637 and are analyzed by a capture detectorto determine cardiac pacing response.

The CRM system 600 may incorporate one or more metabolic sensors 645 forsensing the activity and/or hemodynamic need of the patient.Rate-adaptive pacemakers typically utilize metabolic sensors to adaptthe pacing rate to match the patient's hemodynamic need. A rate-adaptivepacing system may use an activity or respiration sensor to determine anappropriate pacing rate. Patient activity may be sensed, for example,using an accelerometer disposed within the housing of the pulsegenerator. Transthoracic impedance, which may be measured, for example,via the intracardiac electrodes, may be used to determine respirationrate. Sensor information from the metabolic sensor is used to adjust thepacing rate to support the patient's hemodynamic need.

FIG. 7 illustrates a block diagram of capture verification circuitry 700that may be utilized to implement capture verification mode selection inaccordance with embodiments of the invention. The capture verificationcircuitry 700 includes a capture detector 705 that receives signals froman ER sensing circuit. Based on the characteristics of the signalssensed by the ER sensing circuit, the capture detector 705 determinesthe cardiac response to pacing. The capture detector 705 communicateswith other components of the capture verification circuitry 700,including capture verification mode logic/decision circuitry 710, andthe capture verification processor 750 to provide capture detectionacquired during implementation of ACD mode or CTT mode.

As previously discussed, the pacing may be provided to the patient withcapture verification implemented via a plurality of modes, including atleast ACD mode and CTT mode. Capture verification mode logic/decisioncircuitry 710 includes circuitry for selecting between ACD mode and CTTmode, and implementing ACD mode beat by beat automatic captureverification, implementing CTT mode periodic threshold searching withoutintervening beat by beat capture detection, or implementing a fixedvoltage mode or a trend only mode, for example.

Information associated with the efficacy of the ACD mode or the CTT modemay be evaluated by the capture verification processor 750. Prior to theevaluation, the information may be stored in memory 760 for later accessby the capture verification processor 750. The capture verificationprocessor 750 may select an appropriate or desirable captureverification mode based on the efficacy evaluation. If the efficacyevaluation indicates that neither the ACD mode nor the CTT mode isdesirable, the capture verification processor 750 may initiate fixedvoltage pacing implemented using capture verification modelogic/decision circuitry 710, or may initiate a fixed voltage pacing ACDmode circuitry using capture verification mode logic/decision circuitry710, for example.

Various modifications and additions may be made to the embodimentsdiscussed herein without departing from the scope of the presentinvention. Accordingly, the scope of the present invention should not belimited by the particular embodiments described above, but should bedefined only by the claims set forth below and equivalents thereof.

What is claimed is:
 1. A cardiac therapy method, comprising: providingtwo or more capture verification modes including a capture thresholdtest (CCT) mode that performs threshold testing according to a schedulewithout intervening beat by beat capture detection between successivecapture threshold tests; evaluating an efficacy of at least one of theplurality of capture verification modes; and selecting one of theplurality of capture verification modes based on the evaluation.
 2. Thecardiac therapy method of claim 1, wherein the two or more captureverification modes includes a first CCT mode that uses a first CCTalgorithm, and a second CCT mode that uses a second CCT algorithm,wherein the second CCT algorithm is different from the first CCTalgorithm.
 3. The cardiac therapy method of claim 2, wherein selectingone of the capture verification modes comprises selecting the first CCTmode or selecting the second CCT mode.
 4. The cardiac therapy method ofclaim 1, wherein the schedule of the CCT mode includes a regularperiodic time schedule.
 5. The cardiac therapy method of claim 1,wherein the schedule of the CCT mode includes a random time schedule. 6.The cardiac therapy method of claim 1, wherein evaluating the efficacycomprises automatically evaluating the efficacy of the at least onecapture verification mode.
 7. The cardiac therapy method of claim 1,wherein evaluating the efficacy comprises periodically evaluating theefficacy of the at least one capture verification mode.
 8. The cardiactherapy method of claim 1, wherein evaluating the efficacy comprisesdetermining that a condition affecting the efficacy has exceeded athreshold value.
 9. The cardiac therapy method of claim 1, whereinevaluating the efficacy comprises evaluating the at least one captureverification mode with respect to battery longevity.
 10. The cardiactherapy method of claim 1, wherein evaluating the efficacy comprisesevaluating the efficacy based on the occurrence of one or more loss ofcapture events.
 11. The cardiac therapy method of claim 1, wherein thetwo or more capture verification modes includes a first captureverification mode and a second capture verification mode, wherein thefirst and second capture verification modes are associated withrespective first and second pacing energy safety margins, the firstpacing energy safety margin being less than the second pacing energysafety margin.
 12. A cardiac therapy method, comprising: providing aplurality of capture verification modes including: a first capturethreshold test (CCT) mode that performs threshold testing according to aschedule without intervening beat by beat capture detection betweensuccessive capture threshold tests, the first CCT mode using a first CCTalgorithm; a second capture threshold test (CCT) mode that performsthreshold tests according to a schedule without intervening beat by beatcapture detection between successive capture threshold tests, the secondCCT mode using a second CCT algorithm, wherein the second CCT algorithmis different from the first CCT algorithm; evaluating at least one ofthe plurality of capture verification modes; and selecting one of theplurality of capture verification modes based on the evaluation.
 13. Thecardiac therapy method of claim 12, further comprising: executing theselected one of the plurality of capture verification modes according tothe schedule.
 14. The cardiac therapy method of claim 12, wherein thefirst CCT algorithm includes a threshold search that decreases an energylevel of pacing pulses in discrete steps until a predetermined number ofloss-of-capture events occur, and then increases the energy level indiscrete steps until a predetermined number of capture events occurs.15. The cardiac therapy method of claim 14, wherein the second CCTalgorithm includes a threshold search that increases the energy level ofpacing pulses in discrete steps until capture is detected.
 16. Thecardiac therapy method of claim 14, wherein the second CCT algorithmincludes a threshold search that adjusts the energy level of pacingpulses in discrete steps uses a binomial search pattern.
 17. The cardiactherapy method of claim 12, wherein the first CCT algorithm includes athreshold search that adjusts the energy level of pacing pulses indiscrete steps uses a binomial search pattern, and the second CCTalgorithm includes a threshold search that increases the energy level ofpacing pulses in discrete steps until capture is detected.
 18. A cardiacrhythm management system, comprising: a plurality of cardiac electrodes;a pulse generator coupled to the electrodes, the pulse generatorconfigured to deliver pacing pulses to the heart; circuitry configuredto implement a plurality of capture verification modes including acapture threshold test (CCT) mode that performs threshold testingaccording to a schedule without intervening beat by beat capturedetection between successive capture threshold tests; a controllerconfigured to: evaluate an efficacy of at least one of the plurality ofcapture verification modes; select one of the plurality of captureverification modes based on the evaluation; and use the selected one ofthe plurality of capture verification modes until an event is detected.19. The cardiac rhythm management system of claim 18, wherein the eventis related to a loss-of capture.
 20. The cardiac rhythm managementsystem of claim 18, wherein the event is related to a predeterminedschedule.